Method of and apparatus for forming gaseous analysis products from solid samples

ABSTRACT

A TEST APPARATUS FOR FORMING GASEOUS ANALYSIS PRODUCTS FROM A SERIES OF SOLID SAMPLES HAS A RELATIVELY TALL UPRIGHT CRUCIBLE OPEN AT THE TOP AND A CONDUIT EXTENDING WITH CLEARANCE INTO THE CRUCIBLE. THIS CONDUIT HAS A LATERAL INLET INTO WHICH A CARRIER AND/OR REACTION GAS, E.G. O2, IS FED AND THE CRUCIBLE HAS AN UPPER OUTLET ABOVE AND AROUND THE LOWER END OF THE CONDUIT, WHICH IS CONNECTED TO A CHEMICAL-ANALYSIS INSTRUMENT SUCH AS A MASS SPECTROMETER. THE LOWER END OF THE CRUCIBLE IS HEATED AND THE HEATER ELEMENT AND ENTIRE CRUCIBLE ARE COLLED BY A DOUBLE-WALLED JACKET. THE INFLOWING CARRIER FORMS A GAS BARRIER TO THE INFLUX OF AIR. SAMPLES ARE INTRODUCED, ONE AFTER ANOTHER AT SHORT INTERVALS (E.G. 30 SECONDS OR LESS), INTO THE CONDUIT, WITHOUT INTERRUPTING THE GAS SUPPLY OR THE HEATING OF THE CRUCIBLE.

Sept. 26, 1972 w. KOCH ETAL 3,694,157

METHOD OF AND APPARATUS FOR FORMING GASEOUS ANALYSIS PRODUCTS FROM SOLID SAMPLES Filed Feb. 9, 1970 i cEeAM/c GRA PHI T'E /NVN7'0RS: Walter Koch He/muf Lemm 'E/fe/ Voss Peter Hospital Attorney United States Patent METHOD OF AND APPARATUS FOR FORMING GASEOUS ANALYSIS PRODUCTS FROM SOLID SAMPLES Walter Koch, 29 Im Grund, 4000 Dusseldorf-Lohausen,

Germany, Helmut Lemm, 19 Birkenweg, 4231 Blumenkamp, Germany, and Eitel Voss, Duisburg-Hamborn, and Peter Hospital, Walsum, Germany; said Voss and said Hospital assignors to said Koch and said Lemm Filed Feb. 9, 1970, Ser. No. 9,568 Claims priority, application Germany, Mar. 12, 1969, P 19 12 526.9 Int. Cl. G011! 31/12 US. Cl. 23-430 PC 6 Claims ABSTRACT OF THE DISCLOSURE A test apparatus for forming gaseous analysis products from a series of solid samples has a relatively tall upright crucible open at the top and a conduit extending with clearance into the crucible. This conduit has a lateral inlet into which a carrier and/or reaction gas, e.g. O is fed and the crucible has an upper outlet, above and around the lower end of the conduit, which is connected to a chemical-analysis instrument such as a mass spectrometer. The lower end of the crucible is heated and the heater element and entire crucible are cooled by a double-walled jacket. The inflowing carrier forms a gas barrier to the influx of air. Samples are introduced, one after another at short intervals (e.g. 30 seconds or less), into the conduit, without interrupting the gas supply or the heating of the crucible.

FIELD OF THE INVENTION The present invention relates to a method of and apparatus for testing materials. More particularly, this invention concerns a device, and a method of using the device, for releasing gases from solid samples such that gases evolve which can be analyzed by means of mass spectrometry, gas chromatography, infrared absorption, and the like.

BACKGROUND OF THE INVENTION Well-known in the art is a device for carrying out tests of the above-mentioned type which consists of a combustion or reaction tube having fittings at its ends for supplying the reaction and/or carrier gas and for removing entrained released or combustion-generated gas products, means (e.g. induction or resistive-heating elements) for heating the chamber, and a crucible, boat, dish or trough of refractory (generally ceramic) material in which the sample is subjected to heat.

The sample to be tested is introduced into the combustion chamber through a closable port. The sample and the carrying vessel are then, more or less gradually, heated to a temperature sufiicient to sustain combustion or cause gas evolution without reaction with a medium supplied from the exterior. When enough time has passed for the desired gaseous analysis products to evolve, the crucible is flushed with another gas, or the reaction gas, which entrains these products through a conduit to the mass spectrometer or the like. The concentration of the reaction products in the gas medium is measured to determine the composition or the like of the original sample.

Such a device and method is useful for analyzing the composition of metals and metal alloys and especially for carbon and/or sulphur determinations can be readily determined by such methods when oxygen is used as the carrier, thereby reacting with the sample to form CO and ice S0 although the system can be used for N; or H determinations as well.

In general, prior-art devices for producing gases by reaction or evolution of a heated solid body, have the disadvantage that the combustion tube or chamber is of relatively large volume by comparison with the volume of the ceramic vessel in which the sample is held and therefore provides a large space which must be purged of the envolved gases for each analysis. As a result, the evolved gases are sharply diluted with the carrier gas and resolution, i.e. discernment of the products to be analysed, is poor in spite of the high accuracy of the adjunct equip ment used for the analysis. Moreover, the large volume of the chamber necessitates long sparging periods following each heating phase to ensure thorough purging of evolved gases. As a consequence, a heating cycle may require 2 to 3 minutes or more for each sample, a period of time which is unsuited for the needs of the metallurgical industry where samples must be analyzed substantially instantaneously if accurate control of a heat or other metallurgical procedure is to be maintained. Also, time is expended in removing the caps or a cap from the combustion tube and inserting or removing the samples and the vessels (e.g. boats or troughs) containing same. Each procedure requires insertion of the sample in a new vessel and, consequently, loss of heat during the replacement step as well as a heat loss in raising the new vessel to the reaction and evolution temperature. The cost of the relatively expensive ceramic boats is also a problem. What is more, solid portions of the sample, which is usually in powder form, often are entrained also by the carrier. As these dust particles cool, they adsorb some of the gas analysis products, thereby falsifying the final concentration to a relevant extent.

OBJECTS OF THE INVENTION It is, therefore, an object of the present invention to provide an improved apparatus and method of the above described type.

Another object is to provide such an apparatus and method which overcome the abovementioned disadvantages.

It is a further object of our invention to provide a process for generating gases from a solid sample or a series of solid samples in which resolution and accuracy of subsequent analysis steps can be increased, heat losses are reduced, and the sample-processing time lowered, by comparison with earlier systems.

It is another object of this invention to provide an improved system for analysis and breakdown of solid samples, especially metallurgical samples, in which repetitive analyses can be carried out rapidly, economically and conveniently.

It is also an object of the invention to provide an improved analysis system especially for carbon and sulfur determinations of metallurgical samples with improved accuracy.

SUMMARY OF THE INVENTION The above objects are attained, in accordance with features of the present invention, by a testing device having a relatively tall upwardly open crucible into which the lower end of an upright conduit opens. This crucible is formed at its upper end with an outlet and the upright conduit has a lateral inlet between its two ends. Means is provided for introducing a gas, usually 0 into the lateral opening in the conduit such that a portion flows up out of the conduit and a portion flows down in the conduit and into the crucible, thereby forming a gas barrier which is traversable by the same to be tested but which prevents the influx of air down from the upper end of the conduit and into the crucible. This gas introduced into the conduit passes out through the outlet of the crucible, whence it is conducted to a compositiondetermining testing apparatus, such as a mass spectrometer, gas-chromatograph analyser, or infrared absorption apparatus.

In accordance with another feature of the present invention, the crucible is formed as a blind tube having a ratio of diameter to height of around 1:4. The conduit, which is preferably formed at its upper end as a funnel, extends about halfway down into the crucible, with the gap between the mouth of the crucible and the conduit acting as an annular outlet for the evolved gases from the crucible.

Another feature of the invention is that a pair of hollow cylindrical electrodes are provided in the upper region of the crucible to act as a dust trap. One of these sleeves lies against the inner wall of the upper half, approximately, of the crucible, and the other surrounds the lower region of the conduit corresponding to this upper half. In this manner as the mixture of the injected carrier gas and the evolved gases, or the compounds formed thereby, rises up between the two electrodes, any solid material is electrostatically precipitated against one or both of the electrodes. Since the entire crucible is quite hot, these particles do not cool to the temperature at which gas adsorption is possible.

According to another feature of this invention the crucible and heating means, which latter may be a resistance element or inductive heating device, are contained in a hollow-walled element which can be used to insulate them to prevent undue generation of heat into the ambient atmosphere.

Yet another feature of the invention provides for a further conduit axially arranged in the first conduit and utilized to direct a jet of the carrier gas, once again usually oxygen, at the sample in the base of the crucible.

The testing device of the present invention need not be cooled off between every testing operation. What is more, there is no necessity of opening and closing the device to charge a sample into the crucible. For each testing operation the sample need merely be dropped into the funnel-top of the conduit, whence this sample traverses the gas barrier and falls into the crucible. Since the crucible is maintained at its high temperature, the sample quickly is heated up and evolves gases or combines with the carrier gas which is also continuously fed in through the lateral opening of the conduit.

It is an important advantage of the present invention that successive samples may be treated without replacement of the vessel on which they are loaded into the furnace, thereby effecting a saving not only of the cost of the vessel, but also in the time required to insert and reseal the system and the thermal energy necessary to heat such vessels. This feature of the invention consequently provides that the vertically elongated uniform-crosssection cylindrical ceramic crucible be used for a multiplicity of successive sampling operations while being continuously heated and receiving the samples directly through the gas lock or barrel preventing the entry of impure ambient air without impeding the introduction of the samples.

Since the inlet tube reaches a substantial distance into the crucible through its mouth (with an annular clearance defining the outlet passages for the gases), the dimensions of the chamber which must be purged of evolved gases is no greater than the volume of the vessels heretofore used in combustion chambers and frequently even less. The volume which must be flushed free of the evolved gases consequently is a very minor fraction of the volume of the combustion chamber used heretofore so that flushing is complete almost as soon as evolution terminates and the sample treatment time can, therefore, be 30 seconds or less. Since opening and closing of the vessel is not necessary, the successive samples being introduced through the gas curtain, introduction of a subsequent sample can occur as soon as evolution is terminated.

SPECIFIC EXAMPLE 1 g. steel samples containing 0.3% carbon and 0.05% sulfur are introduced in succession into an apparatus of the type shown in the drawing and in which the crucible 1 is composed of Alundum (aluminum oxide). The sample is introduced through a curtain of oxygen fed in through the inlet 6 at a rate of about 2 liter/minute, the crucible being maintained at a temperature of about 2000 C. by resistive heating. Approximately 5000 volt DC. is applied across the cylinders of the electrostatic precipitator. Substantially immediately after contacting the base of the crucible, the sample begins to glow and evolve gases which were entrained to the gas chromatograph where carbon and sulfur content were determined in terms of CO and S0 with close to precision. The gas chromatograph has shown that substantially all evolved gases had been purged from the crucible, within about 30 seconds after introduction of the sample and that substantially no iron oxide particles capable of adsorbing gas, were present in the system. Successive samples were introduced at 30 second intervals and similarly excellent results were obtained. After about 100 sampling processings, however, replacement of the crucible and the cylinders of the electrostatic precipitator was necessary.

DESCRIPTION OF THE DRAWING The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing, the sole figure of which shows, in axial section, an apparatus according to the present invention and, associated devices (shown in diagrammatic form).

SPECIFIC DESCRIPTION The figure shows a testing apparatus having a crucible 1 whose lower region is surrounded by a graphite heating element 2 having an inner axially extending wall 2a connected to one side of a source 12 of electric power and its outer wall 212 connected to the other side of this current source 12.

Surrounding both the crucible 1 and the heating means 2 is a jacket 3 formed with a hollow interior 3a and stepped at 3b to snugly receive the upper end of the crucible 1 and loosely receive the element 2. Air or another cooling fluid circulated by a pump 13 through .a heat exchanger 14 is passed through this chamber 3a to carry off excess heat generated by the element 2. The jacket 3 constitutes the furnace housing.

Formed atop the jacket 3 forming a housing is an internally threaded flange collar 30 into which is screwed a cap 4 formed with a central bore 4a. On O-ring 9 is clamped between cap 4 and the housing 3 such that it is compressed against the outer edge of the mouth of the crucible 1 and thoroughly seals the joint between the cap 4, housing 3, and crucible 1.

A double-walled sleeve 5" is snugly received in the bore 4a, with another synthetic-resin O-ring 15 sealing it therein. This sleeve is shaped much as the element 2, it also has a pair of coaxial cylindrical sleeves attached together at one end and defining an elongated axially extending annular chamber of regular cross section which receives, in the case of the element 5", a graphite sleevelike electrode 10 which has an upper end embedded in a stack of insulating washers 16 and which is connected to one side of an adjustable DC power source 17 whose other side is connected to another graphite sleeve 11 which is snugly received in the top half of the crucible 1 and extends therebeyond into abutting relationship with a step 4b formed in the bore 4a. Although this sleeve 11 is snugly received in the crucible 1, it defines with the bore 4a an annular chamber 19 and has throughgoing bores 18 which permit gas to pass from the crucible into this chamber 19.

The washers 16 are all held together in a metallic cap 20 and define a bore 16a in which the lower end of a short conduit 5' is received, with another synthetic-resin O-ring 21 acting as seal. The upper end 5a of the pipe 5' is formed as a funnel and the pipe 5' with the element 5" together define a straight, upright conduit which is adapted to receive a sample to be tested in its upper end and opens at its lower end into the crucible 1.

The pipe 5 has a lateral opening and branch 6 be tween its two ends. This branch 6 extends immediately adjacent the pipe 5' at an angle a of around 65 to the pipe 5'. This angle a should never be more acute than, say, 45 for reasons which will become obvious below, and the branch 6 should be directed more or less downwardly.

The crucible 1 is advantageously formed of ceramic material, preferably aluminum oxide, in the configuration of a conventional test tube. It has a height H which should be about four times its diameter D. The conduit portion 5" reaches a distance h equal to about one-half of H into this crucible 1.

An oxygen bottle 22 may be connected through a valve 23 to the conduit 6 to feed into the crucible 1 and create the gas barrier preventing influx of ambient air. Furthermore, a conveyor 24 driven by a motor 25 and mounted on a scale 26 or other weighing means is provided to feed samples S into the funnel a.

The cap 4 is formed with a lateral extension 7 having a bore 7a which communicates with the chamber 19 and has a diameter d which is relatively small compared to the diameter D of the crucible and the diameter D of the conduit 5', 5". This extension 7 is connected by a pump 32 to a mass spectrometer 27 in turn connected to a recording device 28.

The above-described device is used as follows:

The pumps 13 and 32 and the power supplies 12 and 17 are activated and the valve 23 is opened to provide a gas flow into and through the crucible 1. Part of the gas goes up after leaving the branch 6 and flows out the mouth 5a of the upper conduit half 5' to create the gas barrier, the remainder goes down through the half 5" into the crucible 1, then up between the electrodes and 11, out through the holes 18, through the passage 7a, and into the mass spectrometer 27.

An adjustable timer 29 actuates the motor 25 to drop .a single sample S, a sample of a steel alloy, for instance, into the funnel 5a. This sample S thence drops through the gas barrier created at the mouth of the branch 6 and falls into the base of the crucible 1. It is immediately heated and, for instance, its carbon combines with the oxygen from the bottle 22 to form CO which is entrained by the 0 up into the spectrometer 27. Any solid particles entrained by the carrier gas are precipitated against the electrode walls 10 or 11 so that they do not reach the passage 7a.

If desired a slim conduit or pipe 8 which is connected through a valve 31 to the 0 bottle can be inserted down through the conduit 5, 5" to insure full combustion of the sample S in the crucible 1 by directing a strong jet of 0 directly against this sample. The reading of the scale 26 is passed by a delay device 30 to the recording device 28 and a computer 33 can also be connected thereto for calculating the composition of the sample. This delay 30 is adjusted so that at the moment when the composition of the sample is marked by the needles of the recorder 28 the weight of this sample is also recorded.

Once the combustion is terminated, usually after 30 60 seconds, the timer automatically actuates the motor 24 to index the conveyor 24 and drop another sample 5 in the conduit 5', 5'.

Samples can be burnt, one on the top of the other, until the crucible is around halfway full; that is, until the residue level reaches the lower end of the conduit 5', 5''.

Cir

This is often after or more tests. Once the relatively inexpensive refractory crucible 1 is filled to this level, the cap 4 is unscrewed and the crucible 1, and usually the electrode 11 also, are discarded and replaced.

While the aforedescribed system has been specifically identified as effective in making carbon and sulfur determinations in the analysis of metallurgical samples, it will be apparent that other analysis processes may make use of the principles and the apparatus. Thus nonmetallic materials may be subjected to gas evolution, merely by thermal breakdown or by combustion or other reactions with the introduced gas or both, to permit analysis of the evolved gases. Also the content of carbon, sulfur and other gasifiable elements in oxidic materials may be established and the system is particularly suited to element-analysis procedures such as fractional total-hydrogen determinations in metallic and oxidic materials. The reactions sustained in the vessel may be reducing as well as oxidizing and, for example, nitrogen determinations in metallic and oxidic materials.

Thermal-breakdown or decomposition analyses include the treatment of limestone samples to evolve CO We claim:

1. A testing apparatus comprising:

an elongated upwardly open crucible having an upper outlet;

an upright conduit generally above the crucible having a lower end opening into said crucible, an upper end adapted to receive a test sample, and a lateral inlet between said ends;

means for introducing a gas into said conduit through said inlet and for forming in said conduit a carrier gas barrier to the influx of air through said upper end into said crucible, said gas entraining gaseous analysis products evolved from said sample from said crucible through said outlet, said barrier being traversable by said sample;

means for heating said sample in said crucible to evolve said products;

a cooling jacket surrounding said crucible and the heating means; and

filter means at said outlet for removing solid particles entrained by said carrier gas, said filter means ineluding an electrostatic filter.

2. The apparatus defined in claim 1 wherein said electrostatic filter includes a pair of substantially coaxial nested sleeves, the outer one of said sleeves lying against the inner wall of said crucible, said outlet being defined between said sleeves.

3. A testing apparatus comprising:

an elongated upwardly open crucible having an upper outlet;

an upright conduit generally above the crucible having a lower end opening into said crucible, an upper end adapted to receive a test sample, and a lateral inlet between said ends;

means for introducing a gas into said conduit through said inlet and for forming in said conduit a carrier gas barrier to the influx of air through said' upper end into said crucible, said gas entraining gaseous analysis products evolved from said sample from said crucible through said outlet, said barrier being traversable by said sample;

means for heating said sample in said crucible to evolve said products;

a cooling jacket surrounding said crucible and the heating means; and

a pipe of smaller diameter than said conduit and axially extending in said conduit, said pipe being connected to the gas-introducing means for directing a jet of said carrier gas against the sample in said crucible.

4. A method of forming a series of gaseous analysis products in an upright combustion crucible open to the atmosphere from a series of solid samples, said method 6. The method defined in claim 4, further comprising comprising the steps of: the step of electrostatically filtering solid particles from continuously heating said crucible; said gas stream. continuously passing a gas stream partly downwardly References Cited 3133251 ifiiiu22 tfin u3$i123 5 UNITED STATES PATENTS top and partly upwardly to form a gas barrier 3,021,199 2/1962 P et 23 230 PC against air influx into said crucible from the atmos- 7/1956 Shlelds et 23 230 PC Phere; 2,809,100 10/1957 Krasl 23 230 PC x successively depositing said sample in said crucible by 10 3244152 4/1966 :Mlxon et ""7 23 253 UX passing them through said barrier while continuing 3529937 9/1970 Ihara 23 230 PC X to heat said crucible and pass said gas stream there- 3173762 3/1965 Varadl et 23 253 PC X through; and 2,465,628 3/1949 Border 23-253 UX training a portion of said gas stream upon each sam 1e v received in Said crucible P 15 J. SCOVRONEK,Pr1mary Examiner 5. The method defined in claim 4 wherein said sample US. Cl. X.R. is deposited into said vessel through a conduit and said 23253 PC barrier is formed in said conduit. 

